CORE D: BODY COMPOSITION, THERMOREGULATION, AND FOOD INTAKE BEHAVIOR CORE ABSTRACT (CORE D) Obesity is the result of an inability to maintain energy balance, and changes in energy balance can also be important contributing factors in the etiology of diabetes and other metabolic diseases. A major goal of Core D (Body Composition, Thermoregulation, and Food Intake Behavior) is to provide investigators with the services necessary to accurately measure the major components of energy balance (energy intake, energy expenditure, body composition, nutrient digestibility) in their mouse models. Core D also provides tests that allow investigators to examine physiological factors that may influence food intake or energy expenditure. In particular, our research team offers services to investigate the role the gut microbiota and epithelial function play in obesity and metabolic disease. The Core D investigators have complementary expertise in energy metabolism, gastrointestinal physiology and gut microbiota and provide clients with assistance in all steps of the research process, from designing experiments to analyzing and interpreting data. In addition to offering standard services in our catalog, Core D also works with investigators to design custom tests or develop new tests to meet their research needs. Based on requests from investigators, we have developed services to determine thermoneutral zone and investigate energy expenditure in response to acute cold or heat stress. We also provide custom, high resolution energy expenditure measurements required to link energy expenditure to specific events (burst of activity, meal consumption, etc.) and accurately determine physical activity energy expenditure, resting energy expenditure and thermic effect of feeding. Core D is currently developing transcriptomic and metabolomic approaches which will expand our microbiota services and provide indicators of microbial function, and we have recently added measures of intestinal barrier function to our catalog of services. Core D will continue to provide our clients with in-depth physiological measurements relevant to body weight regulation while also developing new tests to meet the evolving needs of the research community.